Relationship between impaired parasympathetic and sympathetic cardiovascular control in diabetes mellitus

Impaired nocturnal blood pressure dipping in patients with type 2 diabetes mellitus

Hypertension is a common comorbidity of type 2 diabetes mellitus (T2DM). Both conditions are associated with an increased cardiovascular risk, which is reduced by tight blood pressure (BP) and glycemic control. However, nondipping BP status continues to be an enduring cardiovascular risk factor in T2DM. Cardiovascular autonomic neuropathy and endothelial dysfunction have been proposed as potential mechanisms. This study tested the hypothesis that microvascular disease rather than cardiovascular autonomic neuropathy interferes with the physiological nocturnal BP reduction. Cardiovascular autonomic function and baroreflex sensitivity were determined in 22 type 2 diabetic patients with (DM+) and 23 diabetic patients without (DM-) manifest microvascular disease. BP dipping status was assessed from 24-hour ambulatory BP measurements. Sixteen nondiabetic subjects served as controls (CTRL). Cardiovascular autonomic function was normal in all subjects. Baroreflex sensitivity was lower in DM- compared with CTRL (7.7 ± 3.3 vs. 12.3 ± 8.3 ms·mm Hg^-1; P < 0.05) and was further reduced in DM + (4.6 ± 2.0 ms·mm Hg^-1; P < 0.01 vs. DM- and CTRL). The nocturnal decline in systolic and diastolic BP was blunted in DM- (12% and 14% vs. 17% and 19% in CTRL; P < 0.05) and even more so in DM+ (8% and 11%; P < 0.05 vs. DM- and P < 0.001 vs. CTRL). A nocturnal reduction in pulse pressure was observed in CTRL and DM- but not in DM+ (P < 0.05 vs. DM- and P < 0.01 vs. CTRL). In T2DM, progression of microvascular disease interferes with the normal nocturnal BP decline and coincides with a persistently increased pulse pressure and reduced baroreflex sensitivity, contributing to their increased cardiovascular risk.

Heart rate variability and plasma norepinephrine concentration in diabetic dogs at rest

Cardiac autonomic neuropathy in dogs with diabetic mellitus (DM) was evaluated using measurement of heart rate variability (HRV) and plasma norepinephrine (NE) concentration. Dogs were divided into 2 groups; the control non-DM group (n = 13) and the diabetic group (n = 22) which was further divided into the well-controlled DM (n = 11) and the poorly-controlled DM subgroups (n = 11) according to their fasting plasma fructosamine concentrations. The electrocardiogram (ECG) was recorded continuously for at least 30 min to yield HRV. The results showed that in the poorly-controlled DM subgroup, the average of normal R-R interval (mean N-N), SD of the mean of all 5-min segments of normal RR intervals (SDANN) were lower than the control group while heart rate was higher (P < 0.05). The NNA, SDNN, SDNN index and pNN50% were significantly lower when compared with the well-controlled DM subgroup (P < 0.05). The high frequency (HF) and total power were significantly lower while the ratio of low to high frequency (LF/HF) was higher (P < 0.05) when compared with the well-controlled DM subgroup. Moreover, in the poorly-controlled DM subgroup, plasma NE concentration was lower than the control group (210 ± 37 vs. 479 ± 74 pg/ml, P < 0.05). There was a significantly negative correlation between plasma NE and plasma fructosamine concentrations. It is concluded that cardiac autonomic neuropathy occurred in poorly-controlled DM dogs. The sympathetic activity was suppressed as shown by decrease in both plasma NE concentration and LF component.

Dynamic cerebral autoregulatory capacity is affected early in Type 2 diabetes

Type 2 diabetes is associated with an increased risk of endothelial dysfunction and microvascular complications with impaired autoregulation of tissue perfusion. Both microvascular disease and cardiovascular autonomic neuropathy may affect cerebral autoregulation. In the present study, we tested the hypothesis that, in the absence of cardiovascular autonomic neuropathy, cerebral autoregulation is impaired in subjects with DM+ (Type 2 diabetes with microvascular complications) but intact in subjects with DM- (Type 2 diabetes without microvascular complications). Dynamic cerebral autoregulation and the steady-state cerebrovascular response to postural change were studied in subjects with DM+ and DM-, in the absence of cardiovascular autonomic neuropathy, and in CTRL (healthy control) subjects. The relationship between spontaneous changes in MCA V(mean) (middle cerebral artery mean blood velocity) and MAP (mean arterial pressure) was evaluated using frequency domain analysis. In the low-frequency region (0.07-0.15 Hz), the phase lead of the MAP-to-MCA V(mean) transfer function was 52+/-10 degrees in CTRL subjects, reduced in subjects with DM- (40+/-6 degrees ; P<0.01 compared with CTRL subjects) and impaired in subjects with DM+ (30+/-5 degrees ; P<0.01 compared with subjects with DM-), indicating less dampening of blood pressure oscillations by affected dynamic cerebral autoregulation. The steady-state response of MCA V(mean) to postural change was comparable for all groups (-12+/-6% in CTRL subjects, -15+/-6% in subjects with DM- and -15+/-7% in subjects with DM+). HbA(1c) (glycated haemoglobin) and the duration of diabetes, but not blood pressure, were determinants of transfer function phase. In conclusion, dysfunction of dynamic cerebral autoregulation in subjects with Type 2 diabetes appears to be an early manifestation of microvascular disease prior to the clinical expression of diabetic nephropathy, retinopathy or cardiovascular autonomic neuropathy.

Power spectrum analysis of heart rate variability for cerebral palsy patients

OBJECTIVE

The prevalence of bowel and bladder dysfunction, hyperhidrosis, and poor cardiopulmonary endurance is higher for children with cerebral palsy than for the general population. The purpose of this study was to investigate the autonomic function for patients with cerebral palsy.

DESIGN

Thirty patients with cerebral palsy and 30 control subjects were enrolled in this study. Power spectrum analysis of heart rate variability was performed under standardized conditions.

RESULTS

In both the supine and head-up positions for test subjects, there was no significant difference for the low frequency component of heart rate variability, high frequency component of heart rate variability, or the low frequency/high frequency ratio between the study and control groups. A significantly greater low frequency component of heart rate variability, smaller high frequency component of heart rate variability, and greater low frequency/high frequency ratio while in the head-up position compared with the supine position was noted for the control group, which implies normal sympathovagal balance. A similar phenomenon was not observed for the study group.

CONCLUSIONS

The disturbed balance of activity between the sympathetic and parasympathetic nervous system observed in the study might result from the loss of hemispheric influence in patients with cerebral palsy; however, further investigation is clearly necessary.

Urinary albumin excretion rate is independently related to autonomic neuropathy in type 2 diabetes mellitus

OBJECTIVE

To evaluate if urinary albumin excretion rate (UAER) is independently related to subclinical autonomic neuropathy in type 2 diabetes.

DESIGN

A controlled cross-sectional study.

SETTING

Primary health care centre.

SUBJECTS

Consecutive recently diagnosed (< 1 year) type 2 diabetic patients (group A, n = 150) and patients with long-standing (median 11 years) type 2 diabetes (group B, n = 146) chosen at random. A nondiabetic control group (group C, n = 150) matched for age and gender to group A.

MAIN OUTCOME MEASURES

Neuropathy by cardiovascular reflex tests and UAER by nephelometry.

METHODS

Univariate statistics in group A + B (t-test chi 2- or McNemars test) with Valsalva and breathing ratios as categorical grouping variables and the independent variables gender, smoking, systolic and diastolic blood pressure, fasting serum cholesterol, HDL cholesterol, triglycerides, haemoglobin A1c, glucagon stimulated C-peptide, fasting and postload 1 and 2 h blood glucose and serum insulin, UAER, coronary heart disease and congestive heart failure. Logistic regression analyses in group A + B with Valsalva and breathing ratios as dependent categorical variables and age, systolic blood pressure, congestive heart failure, coronary heart disease, fasting blood glucose, serum triglycerides and UAER as independent variables.

RESULTS

Compared to nondiabetic subjects the diabetic patients of both groups were at increased risk of neuropathy as judged by the Valsalva ratio (P < 0.01). In known diabetic patients with a UAER > or = 30 mg 24-1 h neuropathy was more common than amongst their normoalbuminuric counterparts (Valsalva test P = 0.007, breathing test P = 0.02). In logistic regression analysis UAER independently explained abnormal Valsalva (P = 0.015) and breathing tests (P = 0.04) in the group A + B.

CONCLUSIONS

UAER is independently related to subclinical autonomic neuropathy in type 2 diabetes.

Autonomic neuropathy in asymptomatic subjects with non-insulin-dependent diabetes mellitus and microalbuminuria

Patients with non-insulin-dependent diabetes mellitus (NIDDM) and microalbuminuria (MA) are at increased risk of early death. In NIDDM patients without evidence of heart disease, we examined the links between MA and autonomic neuropathy (AN) and reduced heart rate variability (HRV), both of which have been linked to a poor prognosis. We have studied 43 asymptomatic NIDDM patients with MA and have matched them with 43 normoalbuminuric patients for age, gender, diabetes duration, and smoking status. AN was assessed by heart rate changes to deep breathing, Valsalva, and posture and blood pressure changes to posture and hand grip. Twenty-four hour Holter monitoring was used to evaluate HRV. Patients with MA showed evidence of AN and reduced HRV when compared with normoalbuminuric patients. In multivariate analysis, with measures of AN and HRV as outcome variables, Log albumin excretion rate was a significant independent predictor but stronger predictors were the presence of diabetic retinopathy, age, body mass index, claudication, alcohol consumption, and calcium channel blocker use. The presence of MA is linked to AN and reduced HRV in asymptomatic NIDDM patients. The nature of the relationship is complex, involving multiple relationships with other clinical parameters.

Orthostatic hypotension due to suppression of vasomotor outflow after amphetamine intoxication

Ten hours after ingestion of amphetamines, a previously healthy 17-year-old female adolescent experienced dizziness on standing. Examination revealed pronounced drowsiness and severe orthostatic hypotension. Assessment of arterial baroreflex function suggested that suppressed sympathetic vasomotor drive was the cause of the orthostatic hypotension. Within 3 days, the baroreflex failure resolved spontaneously. To our knowledge, suppressed vasomotor outflow after ingestion of amphetamines has been previously observed only in animal studies.

Effect of chronic mixed pesticide exposure on peripheral and autonomic nerve function

In a cross-sectional study involving 131 flower bulb farmers (mean age = 43 y) and 67 well-matched controls, peripheral and autonomic nerve functions were examined. The study group had been exposed during a period of 20 y (standard deviation = 7) and applied a similar pesticide package. Lifetime cumulative exposure was estimated based on exposure levels for specific application methods and duration of exposure. Exposure-related decreased conduction velocities were found in the motor fibers of the median (-1.1 m/s) and peroneal (fast fibers: -1.2 m/s, slow fibers: -1.3 m/s) nerves, and in the sensory fibers of the median (-1.4 m/s) and sural (-0.9 m/s) nerves. In addition, the refractory period was determined and found to be increased in the sural and peroneal nerves. With regard to the autonomic nerve function, a decrease was found in resting sinus arrhythmia (-10%).

Circulatory autonomic failure 50 years after acute poliomyelitis

A 59-year old woman who presented with postural dizziness 50 years after an acute episode of poliomyelitis is described. There were no new neurological signs and no evidence of motor neuron disease. She had postural hypotension with an abnormal Valsalva. Investigations led to a diagnosis of hypo-adrenergic orthostatic hypotension, with a predominantly preganglionic sympathetic lesion and intact vagal baroreflex pathways. Although pure autonomic failure and multiple system atrophy are possible causes of circulatory autonomic failure, no other new neurological or autonomic features have developed during a 2 year follow-up. We propose that hypo-adrenergic orthostatic hypotension may be a late complication of poliomyelitis. Deterioration in ambulatory ability in a patient with previous poliomyelitis should additionally include assessment of cardiovascular autonomic function.

Cardiovascular responses to tilting in healthy and diabetic subjects

Cardiovascular responses to tilting from supine to upright and back to supine were investigated by measuring heart rate (HR) and blood pressure (BP) continuously by non-invasive methods. Subjects were 20 healthy controls, 17 diabetic patients (DN) with normal test results for parasympathetic cardiac function and 21 diabetics (DA) with abnormal results. In control subjects, tilting up and tilting back maneuvers induced opposite changes in HR, systolic (SBP) and diastolic BP (DBP). The most obvious responses appeared during the first 30 sec after either maneuver. The best measurements to detect sympathetic vasoconstrictor abnormalities during tilting up were derived from the recovery curve that followed the immediate fall in SBP, abnormal in 6 DN and 14 DA patients, and from the increase in DBP after the maneuver, abnormal in 7 and 16, respectively. Tilting back induced comparatively larger cardiovascular responses. The SBP remained stable after 10 sec in the controls, but increased above normal limits in 7 DN and 20 DA patients. The DBP fell during the first 10 sec in controls, but not in 4 DN and 17 DA patients. Continuous monitoring of BP during tilting is a more sensitive test of autonomic function than classical BP measurements made at a few selected intervals. The results challenge the view that parasympathetic dysfunction precedes and occurs more frequently than sympathetic dysfunction.

Chronobiology of catecholamine excretion in normal and diabetic men

The adrenomedullary response to stimuli is often elevated in poorly controlled insulin dependent diabetic patients, and it is controversial whether the adrenomedullary hyperactivity induces the suppression of the circadian rhythm of catecholamines. We have studied the urinary excretion of catecholamines in 11 diabetic patients during 48 h in 4-h collections. Eleven age and weight matched normal subjects served as controls. A circadian rhythm was detected for adrenaline and noradrenaline excretion both in normal and diabetic subjects, with the highest value for both catecholamines in the early afternoon. The mean daily adrenaline levels were significantly higher in diabetic than in control subjects (p less than 0.05). The dopamine excretion was correlated with noradrenaline excretion in normal subjects but did not show a definite circadian rhythm. We conclude that the adrenomedullary hyperactivity does not affect the rhythmic fluctuations of adrenaline and noradrenaline. The dopamine excretion does not show circadian variations and this probably reflects the absence of a single controlling oscillator.

A non-invasive approach to cardiac autonomic neuropathy in patients with diabetes mellitus

The purpose of this study was to obtain information regarding the participation of the sympathetic nervous system in cardiac autonomic neuropathy in patients suffering from diabetes mellitus employing spectral analysis of heart rate variability in the supine and standing posture. Ten insulin-dependent diabetic patients (29 +/- 2 years) with a short to moderately long duration of diabetes (11 +/- 1 years) and cardiac vagal neuropathy based on measurements of respiratory sinus arrhythmia were compared to 10 healthy volunteers (27 +/- 1 years) before and after the administration of atropine and atropine plus propranolol. In diabetic patients the reactivity in total power (delta TP) from supine to upright position was significantly lower compared to control subjects before and after atropine. There was no significant difference in delta TP between diabetics and controls after atropine plus propranolol. The magnitude of TP increase is essentially due to the increase of blood pressure related heart rate fluctuations (delta MF) from lying to standing and dependent on beta-adrenergical efferent activity to the heart. In diabetic patients as well as in normal subjects under the influence of atropine plus propranolol the delta MF power was significantly lower compared to the unmedicated control and atropine group. There was no significant difference between diabetics and controls after combined autonomic blockade. It was concluded that delta MF heart rate spectral power could serve as an indirect, non-invasive, quantitative and sensitive marker of early cardiac sympathetic damage.

Diabetic heart disease--Part II: The clinical and pathological spectrum

Diabetes mellitus is a significant condition, affecting major segments of all population groups studied. With the introduction of insulin and oral hypoglycemic therapy, together with better understanding of diet and weight control gained over the past half century, the primary causes of diabetic morbidity and mortality have shifted in varying proportions from metabolic derangements, infection, and renal insufficiency to different types of cardiovascular disease. Despite extensive clinical and laboratory research on the etiology, pathogenesis, and even the existence of cardiovascular disease associated with diabetes mellitus, however, considerable debate is still apparent in this field. Our purpose is to present an overview of the subject of diabetic heart disease, with a critical analysis of epidemiologic, clinical, and pathological data. Some of this material will be addressed from the perspective of research in this area over the past decade by one of us (SMF), particularly in experimental hypertensive and diabetic cardiomyopathy. However, overall, an attempt will be made to provide an objective and balanced analysis in order to answer the question: does diabetic heart disease exist?

Exaggerated orthostatic hypotension as first sign of diabetic autonomic neuropathy in the elderly

Long-standing diabetic subjects have an impaired sympathetic nervous system activity as a consequence of autonomic neuropathy. Moreover, in this latter group of subjects the parasympathetic rather than the sympathetic nervous system seems firstly impaired by glucose metabolism derangements. In the present study we show that, in aged diabetic subjects with a short duration of the disease (less than 5 years), and who are free from diabetic complications, it is possible to evidence a primary compromise of sympathetic rather than parasympathetic nervous system activity since a greater rate of orthostatic hypotension occurred. In the light of the well-known age-related changes in the physiopathology of cardiovascular activity, we hypothesize that in aged diabetic patients, even after a short duration of disease, sympathetic compromise precedes the derangement of parasympathetic nervous system activity.

Ambulatory and exercise-induced blood pressure responses in type I diabetic patients and normal subjects

We evaluated the ambulatory blood pressure (BP) readings during daily activities and compared the values with the casual office BPs in 12 type I diabetic patients and 12 age-matched, non-diabetic normal controls. The BP responses to 750 kpm/min exercise work load on bicycle ergometer were also evaluated in all the subjects. The mean ambulatory BPs were significantly higher in the diabetic patients compared with non-diabetic subjects. However, the ambulatory and casual office BPs were remarkably similar in each group. Mean peak exercise BPs were higher in the diabetics, but significantly so for diastolic BP (P less than 0.05) and mean arterial pressure (MAP) (P less than 0.01). The mean ambulatory MAP significantly correlated with the casual office MAP in both the diabetics (r = 0.75, P less than 0.005) and non-diabetics (r = 0.58, P less than 0.02). A significantly positive relationship (r = 0.87, P less than 0.001) existed between the ambulatory and peak exercise MAP in the diabetics, but not in the non-diabetic subjects. The mean peak exercise BP responses were significantly (P less than 0.01) higher in the diabetic patients with proliferative retinopathy vs. those with non-proliferative retinopathy. We conclude that casual office BPs reflect the ambulatory values in both diabetics and non-diabetics. Exaggerated BP responses to exercise are found in diabetic patients, especially in the presence of proliferative retinopathy. These findings are suggestive of possible defects in the cardiovascular, autonomic and autoregulatory mechanisms that maintain a normal MAP during daily stresses and exercise in the diabetic patients.

Computerized simultaneous determination of natural age groups for 32 baroreflex arc function parameters and of the corresponding normal ranges for use in the diagnosis of cardiovascular autonomic neuropathy

The diagnosis of diabetic cardiovascular autonomic neuropathy (DCVAN) is based on evaluation of baroreflex arc function (BRAF) by measuring R-R variability at rest and the R-R response to exercises such as the Valsalva manoeuvre, deep breathing, standing up, etc. Using an original computerized technique, we have studied 178 normal subjects (79 males and 99 females uniformly distributed between the ages of 16 and 88 years) so as to determine ages defining natural divisions into 'old' and 'young' groups as regards the values of various BRAF parameters, and simultaneously to determine the natural ranges for each age group so defined. For most of the 32 parameters considered the dividing ages obtained lay between 43 and 55 years. No dividing age could be determined for the response of arterial pressure to the Valsalva manoeuvre or standing up, nor for the mean heart rate while resting in a recumbent position, and in these cases normal ranges were determined for the age range of the whole sample. The effects of aging were not the same for all parameters. Thus instantaneous heart rate variability while sitting at rest and the response to deep breathing (maximum heart rate minus minimum heart rate) both decreased considerably with age, whereas the responses to the Valsalva manoeuvre (PV10) and to standing up (maximum heart rate/minimum heart rate) diminished less markedly. In conclusion, we consider that the reported results accurately establish the normal ranges of the BRAF parameters considered, whose reliability for individual diagnosis of DCVAN is thereby increased.

Autonomic neuropathy: its diagnosis and prognosis

Autonomic neuropathy is now well established as a relatively common and significant complication of diabetes mellitus. Its importance has been clarified in recent years during which the extent of autonomic control over all areas of body function has been defined. Using simple cardiovascular reflex tests, autonomic abnormalities can be demonstrated without any corresponding symptoms. The often stated concept of 'patchy' involvement in diabetic autonomic neuropathy should now be rejected as too should the view that autonomic neuropathy is either 'present' or 'absent' based on a single test result. When generalized and predominantly metabolic disturbances, as in diabetes, give rise to impaired nerve function, autonomic as well as somatic components of the nerve are affected. Where damage is severe this leads to the characteristic florid picture of symptomatic autonomic neuropathy with its particularly poor prognosis. For the physician in a busy clinic, much of the theoretical and experimental basis for autonomic neuropathy may not appear of direct relevance. However, he has now to be aware of the clinical implications of autonomic damage in the diabetic. This may have particular relevance in the care of the diabetic foot (see Chapter 10), the recognition of many of the vague symptoms associated with autonomic damage, the treatment of disabling features such as postural dizziness and nocturnal diarrhoea, and an awareness of the poor prognosis associated with symptomatic autonomic neuropathy. He will also need to be alert to the dangers of general anaesthesia in such patients, and the possibility of sudden unexpected deaths. Diabetic autonomic neuropathy causes widespread abnormalities, some of which are clinically apparent, some of which can be detected by sensitive tests, and others which have yet to be discovered. Inclusion of the neuropeptides and other hormones within the compass of autonomic control has opened up a whole new area of investigative interest, with many complex interrelationships which still need to be unravelled. This should lead to better understanding of the pathophysiological processes that cause damage to diabetic nerves. With so much research effort directed towards better glycaemic control and aldose reductase inhibitors (see Chapter 8), it may eventually be possible to reverse or prevent this potentially disabling and lethal complication of diabetes.

The role of autonomic neuropathy in diabetic foot ulceration

Five standard, non-invasive tests of cardiovascular, autonomic function were performed in each of four groups of 30 subjects: controls, group 1, diabetics without clinical evidence of neuropathy; group 2, diabetics with neuropathy, but without foot ulceration; group 3, diabetics with neuropathic ulceration of the foot. The results showed a significant impairment of autonomic function in diabetics without clinically demonstrable somatic neuropathy compared with controls diabetics with somatic neuropathy compared with those without diabetics with neuropathic ulceration compared with those with neuropathy without ulceration. Parasympathetic function was more seriously affected than sympathetic. In patients who had only mild sensory neuropathy on clinical assessment, those with ulcers had significantly greater impairment of autonomic neuropathy compared with those with uncomplicated neuropathy.

Acute dysautonomia associated with Hodgkin's disease

A patient is described with acute dysautonomia associated with Hodgkin's disease. Testing of cardiovascular reflex control showed that this patient had a rare manifestation of autonomic cardiovascular neuropathy, namely intact parasympathetic heart rate control in combination with a sympathetic postganglionic lesion affecting the control of the vascular tree.

Venous plasma adrenaline response to orthostatic syncope during tilting in healthy men

The effect of transient cerebral ischaemia connected with acute orthostatic hypotension on plasma adrenaline and noradrenaline levels was studied in seven healthy male volunteers during tilt. Sublingual administration of 1 mg nitroglycerin was used to block peripheral vascular reflexes and thus to provoke orthostatic intolerance. A consistent increase in plasma adrenaline concentrations (from 19.2 to 104.3 pg/ml on average, P less than 0.01) was found in six subjects who developed clinical signs of collapse after tilting. Plasma adrenaline never changed after tilting without collapse. Posturally stimulated plasma noradrenaline increases were similar yet irrespective of the presence of collapse.

Diabetes-induced abnormalities in the myocardium

One of the leading causes of mortality in diabetics is myocardial disease. In the past few years this subject has generated a significant amount of interest with the result that myocardial problems associated with diabetes are far better understood. Though originally thought to occur as a result of atherosclerosis, various studies have shown that heart disease can occur in the absence of atherosclerosis, suggesting a diabetic cardiomyopathy. Using diabetic animals, it has been possible to characterize diabetes-induced myocardial abnormalities. Diabetic rat hearts do not respond to conditions of high stress as well as controls. The functional depression is accompanied by altered cardiac enzyme systems. A decrease in myosin ATPase activity which appears to be a result of diabetes-induced hypothyroidism is seen. Also, a depression of sarcoplasmic reticular calcium ATPase, along with a depression of calcium uptake by the SR, is seen in diabetic rat hearts. Na+, K+ ATPase activity has also been shown to be depressed and the depression appears to correlate with depressed atrial contractility. High levels of circulating fats in diabetics may alter the integrity of membranes leading to altered enzyme activities. Insulin treatment has been relatively successful at reversing or preventing myocardial changes in the diabetic rat. Other treatments that have been studied include thyroid hormone treatment, since the depression of myosin ATPase can be corrected by such treatment; and carnitine treatment, as the elevation of long chain acyl carnitines (LCAC) and the resulting depression of calcium uptake in the SR can be so normalized. These treatments have not been successful at normalizing cardiac function. A combination of the two treatments normalized function only partially, suggesting that factors besides myosin ATPase and SR calcium uptake are involved. Other treatments that have been tried include vanadate, methyl palmoxirate, and choline and methionine. Vanadate treatment has proved to be encouraging in that it normalizes both function and hyperglycemia. Methyl palmoxirate, a fatty acid analog, normalized only the elevation of LCAC but did not affect function. Methionine and choline were only partially successful in preventing the functional alterations of diabetic rat hearts. The purpose of the present article is to review our understanding of diabetes-induced myocardial problems and their possible causes. Findings from our laboratory and others are described in which attempts have been made to normalize cardiac function.

Discrimination between cardiac para- and sympathetic damage in diabetics

To analyze the autonomic mechanism on heart rate (HR) variations, pharmacological studies were performed on 8 healthy subjects and 6 diabetic patients. Three HR variations--in supine resting position, during deep breathing in supine position (respiratory HR variations), and on standing (orthostatic tachycardia; delta HR)--were examined. The results in healthy subjects and diabetics were similar. After administration of parasympathetic blockade with atropine, respiratory HR variations were almost abolished. However, no significant difference in delta HR was found. With the addition of beta-adrenergic blockade with propranolol, delta HR was remarkably reduced. Propranolol alone did not affect the respiratory HR variations, but after propranolol administration delta HR was significantly reduced compared with that of the control. The present studies show that respiratory HR variations are predominantly mediated by parasympathicus, whereas orthostatic tachycardia is mediated by both sympathicus and parasympathicus, particularly by sumpathicus. This result suggests the possibility of discriminating the impairment of the 2 cardiac autonomic nervous systems by these simple and non-invasive tests.

Beta-adrenergic blockade may prolong life in post-infarction patients in part by increasing vagal cardiac inhibition

Beta-adrenergic blocking drugs prolong lives of post-infarction patients primarily by preventing sudden cardiac death. The mechanisms responsible for this beneficial effect are not understood clearly, since beta-blockers, in doses used in most clinical trials, are only weakly effective against stable ventricular arrhythmias. Arrhythmias during myocardial ischemia may differ from arrhythmias in other clinical settings in that they depend importantly upon autonomic neural factors, including the balance between levels of sympathetic cardiac stimulation and parasympathetic cardiac inhibition. Beta-blockers reduce sympathetic cardiac stimulation, and they may influence this balance favorably in another important way: a well documented, but not generally appreciated property of beta-blocking drugs is that they also increase levels of vagal cardiac inhibition. I propose that beta-blockade prevents arrhythmic deaths in post-infarction patients in part by increasing levels of vagal cardiac inhibition.

Increased vasopressor responsiveness to angiotensin II in type 1 (insulin-dependent) diabetic patients without complications

The blood pressure response to infused angiotensin II (0.3 to 3 ng X kg-1 X min-1) was investigated in six normotensive patients with Type 1 (insulin-dependent) diabetes free of complications and in six healthy subjects matched for age, sex and weight. Basal blood pressures (111/68 and 114/72 mmHg) and basal plasma angiotensin II levels (18.0 +/- 5.2 and 14.1 +/- 2.4 pmol/l; mean + SD) were similar in the diabetic and control groups as were 24 h urinary excretions of sodium (157 +/- 88 and 154 +/- 84 mmol/24 h). Equal increments in plasma angiotensin II were produced during the infusions in the two groups. Increases in both diastolic and systolic blood pressure were significantly greater in the diabetic patients throughout the infusion. Mean diastolic increments were: 6.7 versus 1.3 mmHg (0.3 ng dose), 11.0 versus 6.9 mmHg (1 ng dose) and 16.7 versus 12.3 mmHg (3 ng dose) (p less than 0.001). Corresponding figures for systolic pressure were: 8.7 versus 1.3 mmHg, 10.3 versus 3.7 mmHg and 15.3 versus 8.7 mmHg (p less than 0.001). Vasopressor responsiveness to angiotensin II is thus increased in Type 1 diabetic patients without complications; it may, therefore, be a consequence of the diabetes rather than of the presence of microvascular disease or hypertension.

Heart receptors for VIP, PHI and secretin are able to activate adenylate cyclase and to mediate inotropic and chronotropic effects. Species variations and physiopathology

We have assessed the presence of VIP/PHI/secretin receptors in heart by: (1) testing the ability of the corresponding peptides to activate adenylate cyclase in cardiac membranes from rat, dog, Cynomolgus monkey and man, and (2) examining the ability of the same peptides to exert inotropic and chronotropic effects on heart preparations from rat and Cynomolgus monkey in vitro. Based on their affinity for natural peptides and synthetic analogs, two types of VIP/PHI/secretin receptors were characterized: the relatively nonspecific "secretin/VIP receptor" of rat heart (that is "secretin-preferring" only in that secretin was more efficient than VIP in stimulating adenylate cyclase), and the "VIP/PHI-preferring" receptor of man, monkey and dog heart. Four physiopathological situations affecting secretin/VIP receptors in rat heart were explored: In male rats from the Okamoto strain and the Lyon strain, two strains presenting spontaneous hypertension, heart membranes exhibited a markedly decreased response of adenylate cyclase to secretin/VIP, with lesser alterations in the responses to isoproterenol and glucagon. This impairment developed in parallel with the occurrence of hypertension and was reproduced in normotensive rats submitted to chronic isoproterenol treatment (but not in Goldblatt hypertensive rats). These findings are consistent with a hyperactivity of norepinephrine pathways in spontaneously hypertensive rats, leading to a reduced number of cardiac post-junctional secretin/VIP receptors bound to adenylate cyclase. Heart membranes from genetically obese (fa/fa) Zucker rats also exhibited severely decreased responses to secretin/VIP with lesser alterations in the responses to glucagon and isoproterenol. These anomalies were specific for the heart, and developed in concomitance with obesity. The first anomaly could not be corrected by severe food restriction. Secretin stimulation of heart adenylate cyclase was also selectively altered in streptozotocin-diabetic rats. Thus, two types of diabetic cardiomyopathy were characterized by a severe local alteration of secretin/VIP receptors coupled to adenylate cyclase. Hypothyroidism, provoked in rat by thyroidectomy or propylthiouracil treatment, again induced a marked decrease in secretin-stimulated cardiac adenylate cyclase activity. In rat papillary muscle electrically stimulated in vitro, secretin exerted a positive inotropic effect. This effect was reduced in obese (fa/fa) Zucker rats. In rat right atrium, secretin also exerted a positive chronotropic effects.(ABSTRACT TRUNCATED AT 400 WORDS)